1. Technical Field
This invention relates to vehicle suspension systems for mounting ground-engaging wheels to a vehicle frame, and, more particularly, to vehicle suspensions having an improved system for mounting a wheel-carrying axle without weakening the axle. In another of its aspects, the invention relates to a trailing arm suspension wherein an axle is mounted to the trailing arm for articulation with respect to the trailing arm.
2. Description of Related Art
The U.S. Pat. No. 3,547,215 to Bird (issued Dec. 15, 1970), discloses a trailing arm suspension wherein a square axle is typically welded to a bracket which is, in turn, secured to the trailing arm of the vehicle suspension structure. The weld securing the axle to the bracket is usually made at the mid-point of the side of the axle where vertical bending moment stresses are neutral. However, these areas are areas of high torsional loading which results from brake torque, vehicle roll and diagonal axle (wheel) walk. The welding at the mid-point of the axle may introduce a point of weakness where cracks can initiate. The weakness in the typical axle welded to a bracket is caused, in part, by the undesirable heat-treating effects and microscopic cracking caused by the welding process upon the axle structure in the localized area adjacent to the weld. In addition, craters or strike marks may form points at which cracks may initiate or at which stresses may become concentrated.
Axles are typically welded to the brackets in order to securely attach the axle to the bracket under this high loading condition. The axle is welded to the axle bracket by a line weld on either side of the bracket. Because it is a line weld, the weld has "ends" at which stresses are concentrated and at which cracks may initiate.
A solution to this weld problem is disclosed in U.S. Pat. No. 4,693,486 to Pierce et al. (issued Sep. 15, 1987), which discloses a trailing arm suspension in which an axle secured to a trailing arm by a wrapper plate partially surrounding the axle, a bolt compresses the wrapper plate about the axle so that the wrapper plate supports and strengthens the axle, and a circular plug weld is positioned on the axle in a circular opening in the wrapper plate to attach the wrapper plate to the axle. Although this system is a significant improvement over the previous welds to the axle, the plug weld still may be a source of stress cracks in the axle.
The U.S. Pat. No. 5,116,075 to Pierce (issued May 26, 1992), discloses a trailing arm suspension wherein a wrapper plate is mounted to an axle through mechanical compression and without welding to the axle. Adapter plates mounted to the ends of the plate apply a compressive force to the corners of a square axle when the wrapper plate is compressed against the axle by a bolt. The wrapper plate is mounted on a pair of side plates which in turn are fixed to the trailing arm. Although the suspension is effective to overcome the potential of crack initiation of the axle between the axle and the axle bracket, the wrapper plate is relatively heavy and a considerable amount of skilled labor is involved in assembling the axle to the trailing arm suspension, frequently at the point of assembly to the axle and suspension to the vehicle. The forces of compression tend to be somewhat uneven. The compressive forces exerted by the adapter plates in particular can be relatively high compared to the compressive forces exerted by the wrapper plate.
The U.S. Pat. No. 5,328,159, Kaufman, discloses a trailing arm suspension in which a pair of U-shaped bracket plates mount U-shaped rubber pads and are clamped onto a square axle with the rubber pads between the bracket plates and the axle. The axle is at a slight angle with respect to the bracket plates so that the bracket plates present a slight diagonal force to the side walls of the axle. The axle is presumably welded to the bracket plates.
The U.S. Pat. No. 5,366,237, to Dilling et al., discloses a trailing arm suspension in which a pair of semi-cylindrical bracket plates are welded to a round axle through an opening between the two plates and along the parting lines between the bracket plates. The axle extends through two openings in the trailing arm and is secured thereto by welding the bracket plates to the beams. The bracket plates are relatively wide and do not deflect when the axle bends. Thus, stress risers can form on the axle at the side edges of the bracket plates. A brake actuator is mounted to the trailing arms for operating brakes on the axle wheels. Welding to the axle can also introduce undesirable microscopic cracks which can initiate fatigue cracks and ultimately lead to failure of the axle due to torsional stress on the axle.
It is also common to mount a track bar between a trailing arm and a central portion of an axle. The track bar is mounted to the axle through a tower bracket which is welded to a central portion of the axle. The welds between the tower bracket and the axle can introduce in the axle weak points and microscopic cracks which can form sources of cracks which may ultimately result in failure of the axle under severe or prolonged loading conditions.
DE 42 32 779 and DE 42 32 778 disclose a vehicle suspension system with an air spring or a leaf spring wherein a relatively square axle is tied in to the suspension through a U-bolt and axle plate which bears against the axle at an upper portion. A filler can be provided in the bottom of the U-bolt. A ring received in an opening in the axle plate is welded to an upper surface of the axle. Frictional force resulting from pressure applied by the axle plate at the upper corners of the axle and by the filler plate at the bottom corners of the axle coupled with the welded ring is said to hold the axle against movement in the mounting. A U-bolt does not give consistent and sufficient compressive forces to adequately prevent slippage of an axle in the mounting and does not work well with round axles.